Field of the Invention
When integrated circuits are fabricated, a plurality of components are formed in a semiconductor substrate. This is typically carried out by doping certain areas of the semiconductor material, which is, as a rule, of one conductivity type. By performing a plurality of such dopant steps, MOS transistors or diodes, for example are fabricated. In the process, masks for covering regions that are not to be doped frequently have to be used, the masks leading to an increase in the number of process steps. When contact is subsequently made with the dopant regions that are produced, further masks are necessary.
One possible way of producing dopant regions is described, for example, in Published, European Patent Application EP 0 480 178 A2. In the publication, a so-called tunnel oxide is deposited on a silicon substrate and a polysilicon layer, which is subsequently doped in a suitable way, is deposited on the tunnel oxide. Under the effect of high temperatures, the dopants which are implanted into the polysilicon layer subsequently pass by diffusion through the tunnel oxide into the silicon substrate and form a dopant region there. There is no provision for contact to be made with the dopant region.